There is a serious need in the plumbing industry to prevent internal corrosion of tubular joints and the invention provides one way to meet this need by the use of cathodic protection. One particular area where the invention has successfully been applied is in the cathodic protection of the internal surfaces of joints between steel nipples employed in water heaters and brass tubing coupled to the nipples through which hot water flows as it is withdrawn from a water heater. The difference in potential between the steel and brass forms a corrosion cell at the joint between the brass and steel which the invention overcomes.